triangle

noun

tri·​an·​gle ˈtrī-ˌaŋ-gəl 

1

: a polygon having three sides compare spherical triangle

2

a

: a percussion instrument consisting of a rod of steel bent into the form of a triangle open at one angle and sounded by striking with a small metal rod

b

: a drafting instrument consisting of a thin flat right-angled triangle of wood or plastic with acute angles of 45 degrees or of 30 degrees and 60 degrees

3

: a situation in which one member of a couple is involved in a love affair with a third person

Illustration of triangle

• 1 equilateral
• 2 acute
• 3 obtuse
• 4 scalene
• 5 isosceles
• 6 right triangle

Examples of triangle in a Sentence

She cut the sandwiches into triangles.

Recent Examples on the Web

At least along the way, there’s a playful love triangle between Julia (Margaret Qualley), the privileged nightmare who’s had Becket wrapped around her pinky finger since grade school, and Ruth (Jessica Henwick), a humble school teacher. —Amy Nicholson, Los Angeles Times, 18 Feb. 2026

His seating position forms a triangle, which Berzock said symbolizes grandeur and status. —Eva Remijan-Toba, Chicago Tribune, 17 Feb. 2026

Catherine Missal Catherine Missal, who plays Lucy's best friend Bree, is the third member of Evan and Molly's onscreen love triangle. —Emma Banks, InStyle, 17 Feb. 2026

Sylvester’s pair features fully red support wings, which typically feature a black triangle on the Fire Red version. —Riley Jones, Footwear News, 17 Feb. 2026

Word History

Etymology

Middle English, from Anglo-French, from Latin triangulum, from neuter of triangulus triangular, from tri- + angulus angle

First Known Use

14th century, in the meaning defined at sense 1

Phrases Containing triangle

• equilateral triangle
• isosceles triangle
• Pascal's triangle
• right-angled triangle
• right triangle
• spherical triangle
• triangle inequality

Rhymes for triangle

• angle
• bangle
• dangle
• jangle
• mangle
• strangle
• tangle
• wrangle
• disentangle
• entangle
• quadrangle
• untangle

Kids Definition

triangle

noun

tri·​an·​gle ˈtrī-ˌaŋ-gəl 

1

: a figure that has three sides and three angles : a polygon that has three sides

2

: a percussion instrument made of a steel rod bent into a triangle open at one corner which is played by striking with a metal rod

3

: a drafting instrument consisting of a thin flat right-angled triangle

Medical Definition

triangle

noun

tri·​an·​gle ˈtrī-ˌaŋ-gəl 

: a three-sided region or space and especially an anatomical one see anterior triangle, carotid triangle, femoral triangle, posterior triangle, suboccipital triangle